1. Field of the Invention
This invention relates to an image forming apparatus, such as a copying machine or a printer, provided with a fixing unit which fixes a developer image on paper.
2. Description of the Related Art
In recent years, in a fixing unit installed in a copying machine using electrophotographic processes, a method using the heat generation of metal by electromagnetic induction has been put to practical use.
One known fixing unit using induction heating is such that, for example, the magnetic flux leaking from the induction coil provided outside the fixing roller is suppressed by a shield member and the heat dissipation of the induction coil is enhanced (Jpn. Pat. Appln. KOKAI Publication No. 2001-313162).
Another known induction heating fixing unit with a exciting coil outside the rotating body is such that the arrangement of a magnetic material on the opposite side of the rotating body of the exciting coil not only increases the heat generation efficiency but also prevents the magnetic field produced from the exciting coil from leaking to the adjoining parts (Jpn. Pat. Appln. KOKAI Publication No. 11-297462).
A further known induction heating fixing unit is such that an induction heating member, a film member for moving the heating member, and an exciting coil fixing member have a ferromagnetic, high-resistivity shield member, thereby preventing electromagnetic noise leaks (Jpn. Pat. Appln. KOKAI Publication No. 9-16006).
Preventing the high-frequency magnetic field generated from the coil from leaking to the outside of the fixing unit prevents the faulty operation of the other devices in the apparatus, including an optionally installed printer controller and FAX controller.
In addition, even when a magnetic field differing in intensity is generated according to the operation mode, the effect of the magnetic field on the other devices in the apparatus is reduced to a minimum.